In writer-director Maya Forbes’s largely autobiographical film Infinitely Polar Bear, opening this week, Mark Ruffalo plays a manic-depressive father who is put in charge of his two daughters when their mother, played by Zoe Saldana, moves from Boston to New York to pursue an M.B.A. It sounds like a setup for disaster, but Infinitely Polar Bear is more gently uplifting, hopeful comedy than depressing family drama. We recently sat down with Forbes and Ruffalo to discuss the making of the film, and some of the valuable themes contained within.

Vanity Fair: Can you talk a little about the origins of the film? How did it come to be?

Maya Forbes: Wes Anderson has been a friend of mine for a long time and I was talking about some idea I had for a movie. It was two girls looking for Sylvia Plath’s lost journal. And Wes said, “You know what? What you’ve got to write about is your dad raising you two girls.” And I thought, Who’s going to be interested in that? You know, sometimes you think your own life isn’t interesting?

Mark Ruffalo: Commonplace.

Forbes: But he wasn’t off base in that I’d always, since high school, I’d been writing about my dad in short stories or essays or something, because I was always wrestling with the mental illness thing. So I did work on the script, and then put it aside, and then work on it, and put it aside, for many years. I guess it wasn’t until I had my own daughters and they turned the age that I was when my father had a big manic break, his big breakdown, and it caused me to reflect on what were the lessons. It was a hard period, and what did I learn from it? Because I was looking at my own daughters, I went into this . . . memory place, where I was seeing them and seeing myself and seeing my life and just thinking about the gifts I’d gotten out of this very hard time, and that’s what sent me going, finally.

Mark how did you get involved? Did you get sent a script that jumped out at you, or did you know Maya already?

Ruffalo: I got a script that really jumped out at me. I read it and felt that it had so much humor and pathos and honesty. And the fact that Maya had written it, and it was her father, and it had such equanimity, that she was so fearlessly looking at him and herself as a kid. I loved it, I thought it was funny, I was really moved by it. And I also thought it would be a great part to play. You can tell a lot about a director by what they write. It’s their first shot at directing a film—there’s three times to direct a film: the writing, the shooting, and the editing. And I felt like the sensibilities were clearly there, so any doubt that you’d have about a first-time director were immediately assuaged. I rarely ever go after a part. I don’t have that much confidence, really? I usually try to talk directors out of giving me parts. I’ll even suggest other actors that would be better for the part, from time to time. But this was one of the very few times where I really felt like, I can do this, I know I can do this, I know I can do a good job, and here’s why. Poor Maya, I really did a full court press on you.

Forbes: I was thrilled! It was amazing. When we met, we really connected.

Ruffalo: Immediately.

Forbes: And I just felt certain that he was the person to do it. The things that weren’t immediately there would be fun to—

Ruffalo: To find.

Forbes: To find, and create. But the core elements were all there.

Ruffalo: I have none of this . . . [Maya’s family] came over on the Mayflower, all right? My family came over here like 20 years ago, in a rowboat. So I didn’t understand that blueblood world, I didn’t understand Boston. None of that I knew, and I knew I was up against a lot.

Forbes: We worked on it for three years. If he was in L.A. or I was in New York, we’d get together. And I would send him videos of my father talking,

Ruffalo: Pictures . . .

Forbes: Any kind of reference material that was helpful. And then when we got to the set, it had sort of percolated.

Oftentimes when mental illness is done on film, there are gimmicks. You know, the sort of sitting in a corner shivering with a blanket—

Ruffalo: Like Avengers 2, you mean?

Right, right. How do you avoid that trap?

Forbes: Seeing movies about mental illness, a lot of falseness has leapt out at me over the years. Sometimes it’s amazing. I mean, I think Tom Wilkinson in Michael Clayton does an amazing job. That really struck me. “Wow.”

Ruffalo: This can work.

Forbes: This can work, you can do this, and make it really real. So I just focused on what I remembered, the real experience of seeing somebody like that. And as an adult, I’ve had family members who are bipolar, so I’ve seen it again. It’s striking to me how it’s a person you know, dialed up. Not a new person, just dialed up. So sometimes it’s right on that edge—are you manic, or are you just being annoying?

Ruffalo: Or happy!

Forbes: Or happy.

Ruffalo: Which is usually very annoying.

Forbes: I find it very annoying. But sometimes, yes, it can be, “Are you just in a great mood?” It’s confusing. So we just tried to focus on who he was.

Ruffalo: On being real.

The movie argues that some of the weirdness the girls experienced was good for them. You guys are both parents yourselves. Do you concern yourselves with that, of how much of yourself, weird or not, you’re bringing into the house?

Forbes: That’s what I was getting at earlier, in terms of starting to write the script. I had these little girls, and I started reexamining what I got out of this period. I feel like I got a lot. There were so many benefits. We’re raising our kids in this culture that’s been pushing fear on you, so hard. Everywhere you go, you have to be afraid. “Your kids are never going to make it.”

Ruffalo: You can’t climb a tree . . .

Forbes: You can’t do anything, you’re never going to make it. I know I can’t absorb that stuff. I was telling my daughters these stories about how I grew up, but also really talking to myself, reminding myself that these kids are resilient, and they are gonna survive. Certainly life will throw difficult things their way. But they’ll handle it. It might be hard, but they’ll get through it, because they’re capable people and they’re gonna figure it out. It’s good to have obstacles and difficulties, and to fail and have things not go the way you want. And then have to figure out how to keep moving forward.

Ruffalo: “What is normal?” really becomes the question. What is normal, and how are we fooled into thinking it’s something other than what we’re doing at any given time. Every family has either a drug addict or an alcoholic or some sort of dysfunction that the family is dealing with. And I think the grace of this family is that they actually could be that far out there but also be forgiving, and be really human, and be human in front of each other without much shame. “Tell them your father is bipolar,” that line in the movie. What we’re saying in the movie is, we live beside it. And we continue to live, we don’t give up anything, we don’t hide it. There’s no shame in it. If my kids can capture that about themselves. . . I have kids with disabilities. All three of my kids are dyslexic, and two of them are ADHD. Now, we could put a lot of shame, and there’s certain schooling that does put a lot of shame, on those aspects, but where they’re going to school now, and the way we’re dealing with it, is to be upfront about it, accepting, and without shame. And those kids are prospering in that environment. And so a home life where it’s so full of so many rigorous ideas about the way things should be, this word “should,” I think is absolutely toxic to children. It hurts their personalities, it hurts their points of view in the world, it hurts their ability to be open and caring and curious. So, yeah. An element of allowance in a family, is, I think, really a positive thing. And clearly! Look at who Cam raised! He raised Maya Forbes, totally viable, working, powerful, strong woman who’s a great mom and is raising great kids herself. And China Forbes who’s a wonderful, celebrated artist. I mean they didn’t do too bad with these kids. Put me in that family first.

Forbes: The not hiding. That was a big revelation for me. My dad said, “You can tell people that I’m manic depressive. You don’t have to hide it.” And once I did, my friends said, “Oh, O.K.” They didn’t care.

Ruffalo: What all the mental health professionals tell you is, this is manageable. You can have a life. This isn’t a death sentence. The difference between that time and the time we’re living in today is management. We’re all managing something or another. I think that’s the hopeful message from the movie.

Mark, what kind of research did you do beyond watching footage of Cameron Forbes?

Ruffalo: Well, I too have manic depressive people in my family. And for a long time it was undiagnosed. Which is really the shame, because they don’t understand what’s happening to them, they’re just always dealing with the consequences. Which is a really lonely life, waking up having to say sorry to people all the time, and feeling almost possessed with this other thing that comes and goes and then leaves their lives in a shambles, but has no label. I was familiar with that. I’ve used this analogy: if you’re an asshole, you’re asshole whether you’re walking out on the street or if you’re in a wheelchair. The same is true of someone who’s bipolar. Really what’s essential was “Who was Cam?” That was the essential thing to figure out, and then we could put him in a wheelchair. But let’s know who he is first. That was essential. Then it was stories, hearing what he did. There was some great stuff that we didn’t put in the movie. One where he swang on a vine, or a rope, through a cocktail party—

Forbes: A garden party.

Ruffalo: A garden party, totally naked, with his mom and dad and all their friends down below. He did some really fun, wild stuff. I hear that and I think “Ohhh, O.K. Now I get a clearer picture.” The other thing I did is really watch people. People in their mania like to post videos of themselves on YouTube. So you can find a lot of videos of people in mania, on YouTube. Then you get the feeling of the energy of mania. That helped me a lot. And I know, I’m more . . . I wish I was manic. I’m more just depressed. I don’t get the fun part. So I really understood what it is to stand in front of the refrigerator with the door open and just going [sighs]. That deadened thing. I understood that. And the mania I picked up along the way.